If FOREST is coded as GNSDTS, how is GARDEN coded?

Explanation

1. 01

   F to G is +1, O to N is −1, R to S is +1, E to D is −1, S to T is +1, T to S is −1.

2. 02

   So the 1st, 3rd and 5th letters move forward 1 and the 2nd, 4th and 6th move back 1.

3. 03

   GARDEN: G to H, A to Z (wrapping), R to S, D to C, E to F, N to M.

4. 04

   The code is HZSCFM.